EPR and electronic spectral studies on Co(II), Ni(II) and Cu(II) complexes with a new tetradentate [N4] macrocyclic ligand and their biological activity

Spectrochimica Acta Part A 60 (2004) 1563–1571

EPR and electronic spectral studies on Co(II), Ni(II) and Cu(II) complexes with a new tetradentate [N4 ] macrocyclic ligand and their biological activity Sulekh Chandra∗ , Lokesh Kumar Gupta Department of Chemistry, Zakir Husain College, University of Delhi, JLN-Marg, New Delhi 110 002, India Received 19 May 2003; received in revised form 12 August 2003; accepted 13 August 2003

Abstract Cobalt(II), nickel(II) and copper(II) complexes having the general composition M(L)X2 (where M = Co(II), Ni(II) and Cu(II), L = ligand, i.e. 3,4,12,13-tetraketo-2,5,11,14,19,20-hexaazatricyclo[13.3.1.16–10 ]cosane; 1(19),6,8,10(20),15,17-hexaene and X stands for Cl− ; NO3 − and SO4 2− ), have been prepared. The structure of the complexes has been elucidated by elemental analysis, molar conductance, magnetic susceptibility measurements, mass, IR, electronic and EPR spectral studies. The magnetic moment measurements of the complexes indicate that the metal ion is in high-spin state. On the basis of IR, electronic and EPR spectral studies an octahedral geometry was assigned for Co(II) and Ni(II) complexes whereas tetragonal geometry for Cu(II) complexes. This ligand and its complexes were also screened against bacteria and pathogenic fungi in vitro. © 2003 Elsevier B.V. All rights reserved. Keywords: Macrocyclic; Cobalt(II); Nickel(II); Copper(II)

1. Introduction The study of macrocyclic complexes is a growing class of research [1–4]. Macrocyclic Schiff base nitrogen donor ligands have received special attention because of their mixed hard–soft donor character and versatile coordination behavior [5,6], and for their biological activities, i.e. toxicity against bacterial growth [7], anticancerous [8] and other biochemical properties [9,10]. In this paper, we report the spectral studies on Co(II), Ni(II) and Cu(II) with a new azamacrocyclic ligand (Fig. 1). On the basis of analytical, magnetic and spectral data an octahedral geometry for Co(II) and Ni(II) while tetragonal geometry for Cu(II) complexes has been assigned. These new compounds were also screened against some bacteria and fungi. 2. Experimental All the chemicals used were of AnalaR grade, and procured from Fluka and Sigma Aldrich metal salts were pur∗

Corresponding author. Tel.: +91-1122911267; fax: +91-1123215906. E-mail address: schandra [email protected] (S. Chandra).

1386-1425/$ – see front matter © 2003 Elsevier B.V. All rights reserved. doi:10.1016/j.saa.2003.08.023

chased from E. Merck and used as received. All solvents used were of spectroscopic grade. 2.1. Synthesis of ligand Hot ethanolic solution (20 ml), of diethyloxalate (2.9228 g, 0.02 mol), and a hot ethanolic solution (20 ml), of 2,6-diamminopyridine (2.183 g, 0.02 mol) were mixed slowly with constant stirring. This mixture was refluxed at ∼76 ◦ C for 8 h in the presence of few drops of concentrated hydrochloric acid. On cooling a solid white colored precipitate formed, which was filtered, washed with cold EtOH, and dried under vacuum over P4 P10 . Yield −75%, mp 269 ◦ C. Elemental analysis found (%) C 51.67; H 3.18; N 25.71. Calculated for Cl10 N6 O4 (atomic mass 326) was C 51.53; H 3.07 and N 25.77%. 2.2. Synthesis of complexes Hot ethanolic (20 ml) solution of ligand (0.6520 g, 0.002 mol) and hot ethanolic (20 ml) solution of corresponding metal salts (0.001 mol) were mixed together with constant stirring. The mixture was refluxed for 5–10 h at

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Fig. 1. Preparation and structure of the ligand (L).

70–88 ◦ C. On cooling, colored complex precipitated out. It was filtered, washed with cold EtOH and dried under vacuum over P4 P10 . 2.3. Physical measurements The C, H and N were analysed on a Carlo-Erba 1106 elemental analyzer. Molar conductance was measured on a ELICO (CM82T) conductivity bridge. Magnetic susceptibility was measured at room temperature on a Faraday balance using CuSO4 ·5H2 O as a callibrant. Electron impact mass spectra were recorded on JEOL, JMS, DX-303 mass spectrometer. 1 H NMR spectra were recorded on Hitachi FT-NMR, model R-600 spectrometer using DMSO as solvent, chemical shifts are given in ppm relative to tetramethylsilane. IR spectra (KBr) were recorded on a FTIR BX-II spectrophotometer. The electronic spectra were recorded in DMSO on Shimadzu UV mini-1240 spectrophotometer. EPR spectra of the complexes were recorded as polycrystalline sample and in DMSO solution, at liquid nitrogen temperature for Co(II) and at room temperature for Cu(II) complexes on E4 -EPR spectrometer using the DPPH as the g-marker. Cyclic voltammograms of the complexes at concentration 10−3 M in the solution of TBAP-DMSO were recorded at room temperature. Redox potential was recorded Ag/AgCl reference electrolyte and glassy carbon as working electrolyte, at the scan rate 100 mV s−1 .

3. Results and discussion On the basis of elemental analysis, the complexes were assigned to possess the composition shown in Table 1. The molar conductance measurements of the complexes in DMSO correspond to non-electrolytes [11]. Thus, the complexes may be formulated as [M(L)X2 ] where M = Co(II), Ni(II) and Cu(II) and X = Cl− , NO3 − and 1/2SO4 2− . The electron impact mass spectra of ligand (L). Fig. 2 confirm the proposed formula by showing a peak at 325 amu corresponding to the macrocyclic moiety [(C14 H10 N6 O4 )+ atomic mass 326]. It also shows a series of peaks, i.e. 32, 56, 107, 163 and 270 amu, etc. corresponding to various fragments. Their intensity gives an idea of stability of fragments. The 1 H NMR spectrum of the ligand does not give any signal attributable to primary diammine or alcoholic protons. The presence of a sharp multiplet in the region δ 8.50–8.62 ppm that is due to the pyrimidine ring hydrogens [12]. Another signal appears in the region δ 7.21–7.33 ppm assigned for the N–H without splitting (4H). No IR spectral bands appear corresponding to the free primary diamine or hydroxyl group, which suggests the complete condensation of keto group with amino group. Four new bands appear in the IR spectrum of the free ligand in the regions 1635, 1531, 1223 and 777 cm−1 assignable to amide I ν(C=O), amide II [ν(C–N) + δ(N–H)], amide III [δ(N–H)] and amide IV [φ(C=O)] bands, respectively [13–15]. Another band appears at 1456 cm−1 assigned for

Table 1 Molar conductance and elemental analysis data of the complexes Complex

[Co(L)Cl2 ]CoC14 H10 N6 O4 Cl2 [Co(L)(NO3 )2 ]CoC14 H10 N8 O10 [Co(L)SO4 ]CoC14 H10 N6 O8 S [Ni(L)Cl2 ]NiC14 H10 N6 O4 Cl2 [Ni(L)(NO3 )2 ]NiC14 H10 N8 O10 [Ni(L)SO4 ]NiC14 H10 N6 O8 S [Cu(L)Cl2 ]CuC14 H10 N6 O4 Cl2 [Cu(L)(NO3 )2 ]CuC14 H10 N8 O10 [Cu(L)SO4 ]CuC14 H10 N6 O8 S

MW Molar conductance Colour (
−1 cm2 mole−1 ) 456 509 481 456 509 481 461 514 486

16 15 12 13 12 15 9 11 13

mp (◦ C)

Magenta 281 Reddish pink 276 Dark brown 292 Green 273 Sky blue 278 Greenish blue 295 Green >300 Pale green 298 Fast green 279

Yield (%) 68 73 75 85 81 72 88 85 74

Elemental analysis data found (calculated) (%) Metal 12.95 11.52 12.16 12.81 11.42 12.13 13.87 12.21 13.21

C (12.92) (11.57) (12.24) (12.88) (11.53) (12.20) (13.79) (12.37) (13.08)

36.73 33.12 34.86 36.95 33.09 34.87 36.61 32.69 34.57

H (36.87) (33.02) (34.94) (36.88) (33.04) (34.96) (36.50) (32.72) (34.61)

2.17 1.93 2.13 2.26 1.95 1.99 2.12 1.93 2.09

N (2.21) (1.98) (2.09) (2.21) (1.98) (2.09) (2.19) (1.96) (2.07)

18.37 22.09 17.53 18.56 22.07 17.46 18.09 21.73 17.19

(18.43) (22.01) (17.46) (18.43) (22.01) (17.47) (18.24) (21.81) (17.30)

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Fig. 2. Electron impact mass spectra of the ligand (L).

Fig. 3. Infrared spectra bands due to anion: (a) [(Co(L)(NO3 )2 ], (b) [Ni(L)(NO3 )2 ], (c) [Cu(L)NI3 )2 ], (d) [Co(L)SO4 )], (e) [Ni(L)(SO4 )], and (f) [Cu(L)SO4 )].

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the pyridine ring, this supports the macrocyclic nature of the ligand and non-shifting of this band in complexes indicate non-involvement of pyridine nitrogen in coordination. A single sharp band observed ∼3289 cm−1 , may be assigned to ν(V–H) of the secondary amino group [10]. The shifting of ν(V–H), in lower side by 10–25 cm−1 , in the complexes, and another feature that the appearance of a new medium intensity band at 463–492 cm−1 attribute to ν(M–N), which provide strong evidence for the involvement of nitrogen in coordination [16]. On the basis of IR spectral study, we conclude that the ligand is tetradentate, coordinate through the four nitrogen atoms of NH group. 3.1. IR bands due to anions IR spectra of nitrato complexes display three (N–O) stretching bands Fig. 3(a–c), at ∼1418–1427 cm−1 (ν5 ), 1303–1311 cm−1 (ν1 ) and 1003–1012 cm−1 (ν2 ). The separation of two highest frequency bands (ν5 − ν1 ) is 107–119 cm−1 . Suggesting that both the nitrate groups are coordinated to the central metal ion [17]. In the sulphato complexes, the presence of two medium intensity bands Fig. 3(d–f), in the region 978–984 (ν1 ), 431–439 (ν2 ). Moreover, another strong band appears in the region ∼1115–1140 cm−1 (ν3 ), which split into two bands that suggest the coordinated behavior [17] of sulphate group in unidentate manner.

4. Cobalt(II) complexes Cobalt(II) complexes show magnetic moment in the range 4.81–4.91 BM corresponding to three unpaired electrons (Table 2). The electronic spectra of all the complexes Fig. 4 (a and b), exhibit absorption in the region 11211–11249 (ε = 79–83 l mole−1 cm−1 ), 14368–14749 (ε = 87–89 l mole−1 cm−1 ), 18182–18692 (ε = 102–105 l mole−1 cm−1 ) and 26316–32362 cm−1 (ε = 141–157 l mole−1 cm−1 ), characteristic for an octahedral geometry [18–21]. The bands may be assigned to the transitions: 4 T1g (F) → 4 T2g (F)— (ν1 ), 4 T1g → 4 T2g —(ν2 ), 4 T1g (F) → 4 T2g (P)—(ν3 ),

Table 3 EPR spectral data of the complexes Complexes

[Co(L)]Cl2 [Co(L)(NO3 )2 [Co(L)]SO4 [Cu(L)]Cl2 [Cu(L)](NO3 )2 [Cu(L)]SO4

Data at room temperature g

g⊥

giso

g

– – – 2.0988 2.1236 (g3 ) 2.1994

– – – 2.0379 2.0483 (g2 ) 2.0789

2.0045 2.0166 2.0148 2.0582 2.0734 (g1 ) 2.0432

– – – 2.6069 2.5590 (R) 0.2285

respectively. The fourth band may be due to charge transfer. In cobalt spin lattice-relaxation times are short, making EPR measurements possible only at very low temperature. EPR spectra of the cobalt(II) complexes were recorded as polycrystalline sample and in DMSO solutions at liquid nitrogen temperature to avoid the broadening of lines at higher temperature (Fig. 5). The deviation in ‘g’ values from the spin only value (g = 2.0023) is due to the angular momentum contribution. g values are listed in Table 3.

5. Nickel(II) complexes At room temperature these complexes show magnetic moment in the range 2.88–2.98 BM. These values are in tune with a high spin configuration and show the presence of an octahedral environment [7] around the Ni(II) ion in the complexes. The electronic spectra of the complexes Fig. 4 (c and d), exhibit three absorption bands in the range 12690–13736 (ε = 3643 l mole−1 cm−1 ), 14493–14706 (ε = 59–62 l mole−1 cm−1 ) and 18692–24038 cm−1 (ε = 113–128 l mole−1 cm−1 ). An examination of these bands indicates that the complexes have an octahedral geometry and might possess D4h symmetry. The ground state of Ni(II) in an octahedral coordination is 3 A2g . Thus, these bands may be assigned to the three spin allowed transitions [22] 3 A (F) → 3 T (F)—(ν ), 3 A (F) → 3 T (F)—(ν ), 2g 2g 1 2g 1g 2 3 A (F) → 3 T (P)—(ν ), respectively. These support an 2g 1g 3 octahedral geometry (Fig. 6).

Table 2 Magnetic moment and electronic spectral data of the complexes Complex

µeff. (BM)

λmax (cm−1 )

ε (l mole−1 cm−1 )

[Co(L)Cl2 ] [Co(L)(NO3 )2 ] [Co(L)SO4 ] [Ni(L)Cl2 ] [Ni(L)(NO3 )2 ] [Ni(L)SO4 ] [Cu(L)Cl2 ] [Cu(L)(NO3 )2 ] [Cu(L)SO4 ]

4.79 4.98 4.93 2.88 2.95 2.98 1.93 2.13 1.98

11211, 11211, 11249, 12690, 13004, 13736, 10460, 10526, 10194,

79, 80, 83, 36, 39, 43, 31, 33, 30,

14368, 18657, 26316 14706, 18692, 32362 14749, 18182 14706, 23474 14493, 24038 14620, 18692, 24155 115074, 22188 15121, 20856 14449, 21739

87, 89, 87, 62, 59, 60, 49, 47, 53,

104, 141 105, 157 102 113 119 128 76 79 74

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Fig. 4. Electronic spectra of the complexes recorded at RT. (a) [Co(L)Cl2 ], (b) [Co(L)(NO3 )2 ], (c) [Ni(L)Cl2 ], (d) [Ni(L)(NO3 )2 ], (e) [Cu(L)Cl2 ], and (f) [Cu(L)(NO3 )2 ].

6. Copper(II) complexes The magnetic moment measurements of the Cu(II) complexes at room temperature lie in the range 1.93–2.13 BM corresponding to one unpaired electron [23,24]. Electronic spectra of the six coordinate copper complexes Fig. 4(e and f), recorded in DMSO, possess absorption bands in the range 10194–10526 (ε = 30–33 l mole−1 cm−1 ), 14449–15121 (ε = 47–53 l mole−1 cm−1 ) and 20856– 22188 cm−1 (ε = 74–79 l mole−1 cm−1 ). These bands may

be considered to the following three spin [17] allowed transitions: 2B 2 A (d 2 2 2B 1g → 1g x2 −y2 → dz )—(ν1 ), B1g → 2g 2 2 (dx2 −y2 → dzy )—(␯2 ) and B1g → Eg (dx2 −y2 → dzy , dyz )—(ν3 ) these transitions suggests D4h symmetry. The energy level sequence will depend on the amount of the tetragonal distortion due to ligand field and Jahn Teller distortion effect. The EPR spectra of Cu(II) complexes were recorded on X-Band at frequency 9.1 GHz under the magnetic field

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Fig. 5. EPR spectra (a and b) recorded at RT in the DMSO solution and (c) recorded at 77 K as polycrystalline sample.

strength 3400 G scan rate 2000, recorded at room temperature. The spectra of the complexes exhibit a single anisotropic broad signal, while splitting occurs in the solution phase, Fig. 5(a and b). The absence of the band for the transition Ms = ±2 can be explained by proposing the interaction between two paramagnetic centers are negligible [25,26]. The study of the spectra give g value in the range

2.0988–2.1236, g⊥ values in the range 2.0379–2.0483. The observed g value for the Cu(II) complexes are less than 2.3. In agreement with the covalent character of the M–L bond. The ratio g > g⊥ > 2.0023 calculated for Cu(II) complexes, suggest that the unpaired electron is localized in dx2 −y2 orbital and the spectral features are characteristic of axial geometry and tetragonally elongated geometry.

Fig. 6. Suggested structure of the complexes.

S. Chandra, L.K. Gupta / Spectrochimica Acta Part A 60 (2004) 1563–1571 Table 4 Ligand field parameters of the complexes Complex

Dq (cm−1 )

B (cm−1 )

β

LFSE (kJ mole−1 )

ν2 /ν1

[Co(L)Cl2 ] [Co(L)(NO3 )2 ] [Co(L)SO4 ] [Ni(L)Cl2 ] [Ni(L)(NO3 )2 ] [Ni(L)SO4 ]

1036.50 1038.44 1010.11 1269.00 1300.40 1373.60

863.75 865.37 841.76 702.81 719.70 723.20

0.77 0.77 0.75 0.67 0.69 0.69

99.07 99.25 96.55 181.93 186.44 196.93

1.28 1.31 1.31 1.16 1.11 1.06

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Ni(III) → Ni(III), Cu(II) → Cu(III) and Ni(II) → Ni(I), Cu(II) → Cu(I) processes, respectively. On comparing the cyclic voltammograms, we observe that the variation in oxidation & reduction potential may be due to distortion in geometry that arises due to different metals in coordination but the difference in E1/2 , value between nickel and copper complexes is less. Which further support to the involvement of (4 N–H) in coordination.

9. Biological screening EPR spectrum of the sulphato complex Fig. 5(c), provide a very good basis for distinguishing between two ground states, of five coordinated structure, i.e. dx2 −y2 (square pyramidal) and dz2 (trigonal bipyramidal) [27]. For the system with g3 > g2 > g1 , the ratio [28] of (g2 − g1 )/(g3 − g1 ), hereafter called the parameter R. if R > 1, predominantly the ground state is dz2 and if R < 1, the ground state will be dx2 −y2 corresponding to square pyramidal structure. The value of g1 , g2 , g3 and R are presented in Table 3. The calculated value of ‘R’ for [Cu(L)SO4 ] indicate a dx2 −y2 ground state, which is consistent with a distorted square pyramidal structure [29]. If the ‘g’ value is greater than 4, the exchange interaction is negligible while a value of ‘g’ less than 4, indicates a considerable exchange interaction in the solid complex. In the complexes of Cu(II) reported in this paper, the ‘g’ value are <4 indicating the sufficient exchange interaction in solid complex.

7. Ligand field parameters Various ligand field parameters were calculated for the complexes and are listed in Table 4. The values of Dq in Co(II) complexes were calculated from transition energy ratio diagram using the ν3 /ν2 ratio. Our results are in agreement with the respective position of anions in the spectrochemical series. The Nephelauxetic parameter β were readily obtained by using the relation: β = B (complei)/B (free ion) where B (free ion) for Co(II) was 1120 cm−1 and for Ni(II), 1041 cm−1 . The values of β and ν2 /ν1 lies in the range of 0.67–0.77 and 1.06–1.31, these values indicate the appreciable covalent character of metal ligand ‘N’ bond.

The ligand (L) and its complexes with Co(II), Ni(II) and Cu(II) were evaluated against some bacteria and pathogenic fungi. 9.1. Antibacterial screening The antibacterial action of the ligand and the complexes of Co(II), Ni(II) and Cu(II) were checked [31] by the disc diffusion technique. This was done on Sarcina lutea (gram-positive), Staphylococcus aureus, Staphylococcus albus and Escherichia coli (gram-negative) bacteria at 38 ◦ C. The disc of Whatmann no. 4 filter paper having the diameter 8.00 mm were soaked in the solution of compounds in DMSO (1.0 mg cm−1 ). After drying it was placed on nutrient agar plates. The inhibition areas were observed after 36 h. DMSO was used as a control and Gentamycin as a standard drug. Hundred percent growth of bacteria which is represented as +, 50% growth by ++, less then 50% growth by +++ and noble inhibition by ++++. The bacterial growth inhibition capacity of the complexes follow the order Cu(II) > Ni(II) > Co(II), given in Table 5, Fig. 7(a). The antifungal activity of the ligand and its complexes was checked, by the agar plate technique [32] for the Agaricus fulviceps, Ustilago hordei, Aspergilius niger and Paziza catinus fungi. The compounds were directly mixed to the medium in different concentrations. The fungus was placed on the medium with the help of the inoculum needle. The petri dishes were wrapped carefully in polythene sheets, containing some drops of EtOH and put in an incubator at 34 ± 4 ◦ C for 74–96 h. The growth of fungus was measured by the recording the diameter of fungal colony. The following relation calculated the fungal growth inhibition:

8. Electrochemical behavior

fungal growth inhibition (%) = ((A − B) × 100)/A

The cyclic voltammograms of Ni(II) and Cu(II) complexes in 103 M TBAP-DMSO solution were recorded at room temperature. Redox potentials were recorded in Ag/AgCl [30] using a glassy carbon as working electrode. The microelectrode radius was 5.0 ␮m and the scan rate was 100 mV s−1 . The typical cyclic voltammograms of [Ni(L)Cl2 ] and (Cu(L)Cl2 ]. The complexes exhibits two one electron quasi reversible peaks, corresponding to the

where A is the diameter of fungal colony in control plate, and B is the diameter of fungal colony in test plate. Hundred percent growth of fungus which is represented as ∗ , 50% growth by ∗∗ , less then 50% growth by ∗∗∗ and noble inhibition by ∗∗∗∗ . The results of antifungal activity are shown in Table 6. The ligand (L) and Co(II) complexes show a moderate activity against all the species studied here. Nickel(II) complexes show comparatively better inhibition while an excel-

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Table 5 Antibacterial activity data of the ligand and complexes Compound

Bacterial inhibition (%) Sarcina lutea

Staphylococcus aureus

Staphylococcus albus

Escherichia coli

Ligand (L) [Co(L)Cl2 ] [Co(L)(NO3 )2 ] [Co(L)SO4 ] [Ni(L)Cl2 ] [Ni(L)(NO3 )2 ] [Ni(L)SO4 ] [Cu(L)Cl2 ] [Cu(L)(NO3 )2 ] [Cu(L)SO4 ]

++ + ++ + +++ ++ +++ ++++ +++ +++

++ ++ + ++ ++ +++ +++ +++ ++++ +++

+ + ++ + +++ ++ ++ ++++ +++ ++++

++ ++ + ++ ++ +++ +++ +++ ++++ +++

Fig. 7. Biological activity of the ligand and the complexes. (a) Antibacterial action and (b) antifungal activity.

lent toxicity against fungal growth, studied here, was shown by Cu(II) complexes Fig. 7(b). The ligand presented here and its transition metal complexes gives better results against the growth of bacteria and

fungi then the some other work reported earlier [31,32]. That means by further study and development, some of these compounds may be used as a better toxic agent against bacteria and fungi.

Table 6 Antifungal activity data of the ligand the complexes Compound

Ligand (L) [Co(L)Cl2 ] [Co(L)(NO3 )2 ] [Co(L)SO4 ] [Ni(L)Cl2 ] [Ni(L)(NO3 )2 ] [Ni(L)SO4 ] [Cu(L)Cl2 ] [Cu(L)(NO3 )2 ] [Cu(L)SO4 ]

Fungal inhibition (%) Agaricus fulviceps

Ustilago hordei

Aspergillus niger

Paziza catinus

** * ** ** ** *** ** *** **** ***

* ** * ** *** ** *** **** *** ***

** * ** * ** ** ** *** **** ***

* ** * * *** *** ** **** *** ****

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Acknowledgements We are thankful to the Principal, Zakir Husain College for providing laboratory facilities and IIT Mumbai for recording EPR spectra. We also express our best thanks to UGC, New Delhi, for financial assistance.

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